When the surface moisture on particulate solids freezes, the ice acts as a powerful adhesive holding the particles together in a mass, e.g., crushed coal, which with as little as four percent moisture will, when frozen, cohere so strongly as to require special handling to break up the frozen mass. It thus becomes difficult to unload or dump railway cars, trucks and other conveyances used to transport coal, mineral ores and other finely divided solids. It also makes difficult the conversion of the outdoor coal storage piles unto a condition for fuel or other use. Unloading frozen coal from railroad cars is time consuming, can result in blocked dump chutes and can often leave as much as 30 to 60 tons of coal in the car. Various techniques such as vibration, steam lances, fires under the cars, infrared heating in warming sheds and even dynamiting have been tried to unload frozen cars. Another approach is to chemically modify the environment contiguous with the particulate surfaces. Sodium chloride and calcium chloride salts have been added to moist coal as it is being loaded with some degree of success toward reducing the freezing problem. However, such salts contribute to the corrosion of all equipment with which the solids come in contact and are detrimental to the coking process when used with coking coal. Oil has been used to freeze-proof coal with questionable effectiveness. Oil soluble surfactants have been added to the oil but with questionable results. Ethylene glycol has been employed, but although successful, the cost of treatment has been very high.
Referring now to the patent literature there is included:
U.S. Pat. No. 4,117,214 which teaches a composition for reducing the strength of ice featuring a mixture of (A) a water-soluble polyhydroxy compound of a monoalkylether and (B) a water soluble organic nonvolatile compound having a hydrophilic group such as amine, carboxyl or carboxylate, said mixture used in an effective amount, e.g., on the order of about 0.25-5 weight percent, based on the weight of water;
U.S. Pat. No. 3,298,804 is directed to the prevention of freezing together of coal particles by a composition of hydrocarbon and a given class of surface-active compounds;
U.S. Pat. No. 3,563,714 is not concerned with freezing but compacting coal particles, however, it teaches spraying coal with a water-in-oil emulsion obtained from a blend in oil of surfactants having an average hydrophilelipophile balance of 10 or less;
U.S. Pat. No. 3,794,472 treats coal with an aqueous emulsion containing a polyhydric alcohol to prevent freezing.
U.S. Pat. No. 4,225,317 treats the coal by spraying coal particles prior to freezing with an effective amount of a hydrocarbon liquid solution of a nonionic surfactant having an HLB between 9.5 and 11.0.
In a co-pending U.S. patent application Ser. No. 508,527, filed June 27, 1983 (now abandoned) which was a Continuation Application of Ser. No. 318,484 filed Nov. 5, 1981 (now abandoned) (of common assignee with this application) there is taught a method for treating particulate solids such as coal having surface moisture which comprises spraying such solids with a minor but at least effective amount of a hydrocarbon liquid solution of a mixture of an anionic surfactant, i.e., a water soluble salt of an alkyl aryl sulfonic acid, and a nonionic surfactant such as dinonylphenol reacted with 9 moles of ethylene oxide, said mixture having an HLB of at least 12.